1. Field of the Invention
The present invention relates to a one-component developing device used for an electrophotographic apparatus, such as a copier or a printer, and relates in particular to a one-component developing device which uses a one-component developer.
2. Related Arts
Currently, electrophotographic apparatuses are employed as copiers or printers. Such an electrophotographic apparatus forms an electrostatic latent image on a photosensitive drum, and then develops the latent image, a task for which a developing device is required. In general, two types of devices are employed for this purpose: a two-component developing device and a one-component developing device, which respectively use a two-component developer and a one-component developer. Of the two devices, the one-component developing device is the least complicated to make and the one can be constructed the most compactly. But when a one-component developing device is used, the layer of developer with which a developing roller is coated must have a uniform thickness.
FIG. 11 is a diagram showing a conventional developing device.
As is shown in FIG. 11, an electrostatic latent image is formed on a latent image bearing member 90, such as a photosensitive drum, and the latent image on the latent image bearing member 90 is then developed using a one-component developing device 91. The components comprising a one-component developing device 91 include a developing roller (developer carrier) 92, a feed roller (developer feeding member) 94, and a regulating blade (developer regulating member) 93.
In the development process, a one-component developer 95 is used to uniformly coat the developing roller 92, which then transports the developer 95 to a developing area, facing the photosensitive drum 90, where in response to the application to the developing roller 92 of a bias voltage (a DC or an AC voltage), developer 95 is transferred to the photosensitive drum 90. For this process, the feed roller 94 supplies the developer 95 to the developing roller 92, and the regulating blade 93, which is formed of a stainless steel leaf-spring, smooths and levels the developer 95 on the developing roller 92.
In a conventional developing device, a uniform thickness is maintained for the coating of the developer 95, which is supplied to the developing roller 92 by the feed roller 94, by the regulating blade 93. And the developing roller 92 is rotated so that it transports the developer 95 to the developing area for the photosensitive drum 90.
The arrangement of a one-component developing device can be simplified. In such a device, the regulating blade 93 is formed of a leaf-spring, which at one end is fixed to the frame of the developing device and at the other end is free. With this arrangement, based on the support provided by its fixed end, the regulation blade 93 is pressed against the developing roller 92 by the force developed by the leaf-spring and maintains on the developing roller 92 a developer 95 layer having a constant thickness. Accordingly, the blade 93 linearly contacts the developing roller 92.
However, the conventional developing device has the following problems.
First, in order to increase the quantity of available developer 95, the amount supplied must be sufficient to fill the space behind the regulating blade 93. For especially when a developing unit is supplied as an exchangeable cartridge, if a large quantity of developer 95 is loaded into the cartridge the replacement period can be extended, and running costs can be reduced. However, because under the circumstances the developer 95 is stored to the rear of the leaf spring regulating blade 93, the pressing force exerted by the blade will vary in accordance with the amount of developer 95 remaining in the cartridge. In other words, when there is a large amount of developer 95 available to the rear of the regulating blade 93, the force with which the regulating blade 93 presses against the developing roller 92 is comparatively strong; but as the supply of developer 95 is depleted, there is a corresponding reduction in the pressing force exerted by the regulating blade 93.
Therefore, the thickness of the developer layer on the developing roller 92 varies, and image density is accordingly changed. To prevent this, the maximum volume of the developer must be reduced so that undue pressure is not applied to the regulating blade 93; however, when the maximum volume for the developer is reduced, the replacement period is shortened. And although the size of the developer unit may be increased so it contains more developer, such an increase will result in a like increase in the size of a printer itself.
Second, when a large amount of developer 95 is supplied, in addition to influencing the pressing force exerted by the regulating blade 93, the developer 95 tends to compact and to form solid masses which thereafter are attached to the regulating blade 93. As a result, the thickness of the developer 95 applied to the developing roller 92 is not uniform, and lines and stripes appear on a developed image.